This invention relates to polyphase transverse flux dc motors and in particular, but not solely, motors of the xe2x80x9cinside outxe2x80x9d type where the rotor rotates externally of the stator.
The use of term xe2x80x9cpolyphasexe2x80x9d in relation to a dc motor means a motor with a plurality of windings, or a plurality of sets of windings, which when excited sequentially from a dc source produce a rotating flux. Commutation of the motor phases is normally achieved using electronic switching devices in a bridge arrangement with the switching sequences controlled by a micro-processor.
The advantages of transverse flux machines are well known. A transverse flux machine is capable of producing power densities several times greater than conventional electrical machines. This arises from the geometry of transverse flux motors which enables a larger number of poles while maintaining the same magnetomagnetic force (MMF) per pole as would be achieved in a conventional machine design.
Transverse flux machines have in the past been difficult to implement because standard core lamination techniques do not easily permit the three dimensional. magnetic flux flow required in transverse flux machines. This difficulty is being overcome by the use of sintered powdered iron cores. These may be formed by a compression moulding technique.
Most transverse flux machine configurations disclosed hitherto are single phase machines. An example is disclosed in U.S. Pat. No. 5,773,910 (Lange). Proposals for polyphase machines usually involve complex geometries which lead to difficulties in manufacture. For example U.S. Pat. No. 5,117,142 (Von Zueygbergk), U.S. Pat. No. 5,633,551 (Weh) and U.S. Pat. No. 5,854,521 (Nolle).
It is therefore an object of the present invention to provide a polyphase transverse flux DC motor which is simple to manufacture.
Accordingly in one aspect the invention consists in a polyphase transverse flux dc motor comprising:
a rotor having alternating magnetic pole polarities at the periphery; and
a stator mounted co-axially with said rotor so as to provide at least one air gap there between, said stator including:
a first stator piece having a plurality of circumferentially disposed and spaced apart claw poles projecting in an axial direction,
a second stator piece complementary to said first stator piece and mounted co-axially in facing relationship with said first stator piece such that there is an axial spacing there between and oriented about the common axis such that the claw poles of the second pole piece circumferentially alternate with the claw poles of the first pole piece;
a plurality of magnetically permeable bridging cores disposed about the stator axis proximate to said claw poles and located between said first and second stator pieces to provide magnetic flux paths there between,
at least one said stator piece being provided with regions of magnetic high reluctance between the sites of said bridging cores, and
stator windings disposed about each bridging core each of which when supplied with an exciting current produce flux flow through those stator claw poles in the first and second pole pieces which are proximate to the corresponding bridging core thereby producing flux in said air gap adjacent such claw poles, each winding or a selected set of windings constituting the windings for one of a plurality of motor phases which in use are electronically commutated to produce a flux in said air gap which rotates about the stator axis.
In a further aspect the invention consists in a polyphase transverse flux dc motor comprising:
a rotor having a plurality of permanent magnets circumferentially disposed and separated by magnetically permeable material to provide alternating magnetic pole polarities at the periphery, said magnets being magnetised in the circumferential direction; and
a stator mounted co-axially with said rotor so as to provide at least one air gap therebetween, said stator including:
a first stator piece having a plurality of circumferentially disposed and spaced apart claw poles projecting in an axial direction,
a second stator piece complementary to said first stator piece and mounted co-axially in facing relationship with said first stator piece such that there is an axial spacing therebetween and oriented about the common axis such that the claw poles of the second pole piece circumferentially alternate with the claw poles of the first pole piece,
a plurality of magnetically permeable bridging cores disposed about the stator axis proximate to said claw poles and located between said first and second stator pieces to provide magnetic flux paths therebetween,
at least one said stator piece being provided with regions of magnetic high reluctance between the sites of said bridging cores, and
stator windings disposed about each bridging core each of which when supplied with an exciting current produce flux flow through those stator claw poles in the first and second pole pieces which are proximate to the corresponding bridging core thereby producing flux in said at least one air gap adjacent to such claw poles, each winding or a selected set of windings constituting the windings for one of a plurality of motor phases which in use are electronically commutated to produce a flux in said air gap which rotates about the stator axis.
In a further aspect the invention consists in a method of making a stator for a polyphase transverse flux dc motor, comprising the steps of:
forming a first stator piece having a plurality of circumferentially disposed and spaced apart claw poles projecting in an axial direction,
forming a second stator piece similar and complementary to said first stator piece, providing a plurality of magnetically permeable bridging cores to be symmetrically disposed about the stator axis proximate to said claw poles between said first and second stator pieces to provide magnetic flux paths therebetween,
providing regions of high magnetic reluctance between the sites of said bridging cores in either or both of the first or second stator pieces,
placing stator windings about each bridging core,
assembling the first and second stator pieces co-axially in facing relationship with each other and spaced axially apart by said bridging cores with said second stator piece oriented about the common axis such that the claw poles of said second pole piece circumferentially alternate with the claw poles of said first pole piece;
each said winding or a selected set of said windings constituting the windings for one of a plurality of motor phases such that in use when supplied with an exciting current produce flux flow through those stator claw poles in the first and second pole pieces which are proximate to the corresponding bridging core.
In yet a further aspect the invention consists in a polyphase transverse flux motor including a rotor having a plurality of circumferentially disposed permanent magnets separated by segments of high permeability material to form rotor poles,
a stator mounted co-axially with said rotor so as to provide at least one air gap therebetween, said stator having a plurality of circumferentially disposed and spaced apart poles,
at least one stator winding per phase disposed such that when supplied with an exciting current produce flux flow through stator poles which are proximate thereto to produce a flux in said air gap adjacent to said poles, said windings in use being electronically commutated to produce a flux in said air gap which rotates about the stator axis,
the improvement defined by the relationship wherein the number of motor phases (P) is selected from the series 2, 3, . . . , N, the number of windings per phase (W) is selected from the series 1, 2 . . . M, the number of poles associated with each winding (PW) is selected from the series 2, 4, . . . 1, and the number of stator poles (SP) is equal to the product P*WP*PW and the number of rotor poles is SPxc2x1W.